CB550 Fuel flow question

I have a 1974 CB550. It runs great for a few minutes, then it will
start to run rough, like it is not running on all cylinders. I check
the fuel filters and one is full, the other is dry.

I tested the flow from the fuel valve by connecting to fuel lines into
a gas can. When I turn open the fuel valve, the following occurs
which may or may not be normal.

When I open the valve, fuel flows from line A but nothing from line B.

If I plug line A with my finger, then fuel begins to flow from line B.

I release line A fuel is still only flowing from line B nothing from
line A.
I plug line B with my finger and fuel begins to flow from line A again
Now if I release line B, fuel will flow from both lines.
If I turn the valve off, then on, fuel is only flowing from line A
again.

I can repeat this process every time. I’m not sure if this is normal
or not.

I have completely taken apart and cleaned the petcock, it now looks
brand new inside. There are no leaks.

Part of getting the bike ready to ride this year included buying a new
set of carbs that were already rebuilt. I put them on and adjusted
the sync and the idle. I have not made any other adjustments to the
carbs.

Is there something else to adjust that will help the fuel flow or
should I try to replace the petcock?

Thanks

John

 

Steady now, here seems to be a misunderstanding. There is
only 1 (one) fuel hose from the petcock (or it's the weirdest
one I ever saw). The other hose is a vacuum line to operate
the petcock.
The fuel flow that you get out of the vacuum hose means
that the membrane that opens the petcock is broken and
needs to be replaced.
Fuel should only flow with the petcock in "P" / "pri"
position or when there is vacuum (the engine is running).

 

try it with the fuel tank filler cap open (or off). I've seen strange
things happen and sometimes a vacuum occurs if the cap cant be vented
do to crud build up. You may be getting some vacuum from one side but
not the tank itself. It's a long shot but would be cool if that's all
it was.
good luck,
walt

 

This must be a wierd one, because there are 2 fuel lines, one connects
between carb 1&2 and the other connects between carb 3&4. I don’t
have a "PRI" position, just On, Off, and Reserve.

I am just curious if this is normal operation or not, because I would
expect that fuel runs from both lines as soon as you open the valve.

 

i haven't seen a petcock with a vacuum line from 1974. The set up you
have sounds correct to me. Two lines that get split between the two
sets of carbs. They should flow together unless there is some sort of
vacuum preventing them to flow. If your fuel tank wasn't vented it
would let one side flow while the other sucked air.
If you remove your gas cap and it still didn't work correctly i would
assume it is the petcock itself.
Good luck, (sounds like you could use some!)

walt